The present invention relates generally to an internal combustion engine including a mass airflow based control system and, more particularly, to an improved method and apparatus for controlling an internal combustion engine which is capable of inferring barometric pressure surrounding the engine.
In order to optimally control an internal combustion engine, it is necessary to accurately know the barometric (atmospheric) pressure surrounding the engine. Barometric pressure is used, for example, to determine the amount of fuel needed during initial cranking of the engine. Further, exhaust gas recirculation (EGR) and spark control are normally adjusted versus barometric pressure to achieve desired emissions requirements, fuel economy and drivability.
In the past, engines having mass airflow based control systems have obtained barometric pressure readings by employing barometers, which sense the barometric pressure surrounding the engine. Adding a barometer to a control system, however, is disadvantageous because of the added expense of an additional sensor. Further, it complicates the system design with additional wiring and ties up the use of an additional input channel to the engine controller.
U.S. Pat. No. 4,600,993 discloses a speed density control system which includes a manifold pressure sensor, and teaches inferring barometric pressure from manifold pressure sensor readings. However, since mass airflow based control systems do not normally employ manifold pressure sensors, such a method of inferring barometric pressure is not applicable to mass airflow based systems.
Accordingly, there is a need for an improved mass airflow based control system which is capable of determining barometric pressure surrounding an internal combustion engine without employing a barometer.